Here are some tips for creating a fuzzy illuminated scarf with color-changing LEDs, with a relatively simple process that is suitable for someone with limited sewing or soldering experience.
The lens of each of these RGB LEDs contains its own red, green, and blue emitters, and a built-in processor to make it blink or fade between colors, so you can achieve a fairly sophisticated effect with a simple circuit, and no external driver. The flexible connecting wires are concealed by a fabric lining, so the finished product is very comfortable and easy to wear. The lights create a nice diffused glow in the fur - wear it as a conversation piece, fashion statement, or safety accessory.
The number of lights in the design can be scaled up or down, with no need for a current-limiting resistor, although battery life will decrease as you increase the number of lights (unless you upgrade to a larger 4.5V supply).
Step 1: List of materials
piece of faux fur for scarf (60" x 9" for the example shown)
fabric for lining (60"x9", or can be more of the same fur)
extra fabric for battery pocket
strip of velcro, approx 3" long
razor blade (to cut fur, optional)
sewing machine (optional)
buttons (standard 2-hole sewing type, approx 1/2" diameter - not rubber, not metal. most plastic buttons are reasonably heat resistant. available at craft stores, or by the pound at buttons4u.com)
Electronic materials and tools:
color-changing RGB LEDs (the type with a built-in flashing or fading circuit, with two external leads - a fast blinking version is available at allelectronics.com, slower fading versions are available on eBay)
battery holder for 3 AA cells, batteries
on/off switch (optional) SPST pushbutton (non-momentary)
insulated connector wire (stranded wire in the range of 20-24 GA - can be obtained by separating pieces from standard ribbon cable)
helping hand stand with spring-loaded clips
Other stuff you'll need:
soft surface for pressing LEDs into buttons while bending leads (electrostatic work mat or yoga mat)
hot glue gun and glue sticks
pen or marker
Step 2: Plan light layout
In these directions, we assume that a battery voltage of 4.5V will be supplied to the scarf (from 3 AA cells), and that all of the lights are connected in parallel with no current limiting resistor. The battery pack will be mounted near one end of the scarf, where the weight is not particularly noticeable compared to the weight of the faux fur.
Other variations are possible, of course - you can mount your batteries near the middle of the scarf, or use a higher driving voltage (such as 9V) and split the lights into two groups that are wired in series.
Battery life will depend on the number of lights and the battery type. A pack of 3 AA cells will power 50 RGB LEDs for several hours.
Step 3: Cut fabric
The scarf shown here has dimensions of about 60" by 9". We chose the 60" measurement to match the typical purchased fabric width of 60". If your fabric width is 45", you can make a shorter scarf or piece the fabric together. Save some extra fabric for the battery pocket that you'll build in step 9.
To cut faux fur with a minimal amount of shedding, use a razor blade on the back surface. Then, reduce shedding further by finishing the edges of the fur with a serger (overlock sewing machine) or a zigzag stitch.
Step 4: Poke LEDs through fur, secure with buttons
If you have trouble poking the leads through, or they seem to bend too easily, you can make them sharper with wire cutters by trimming the leads at a 45 degree angle. It is important to maintain a difference in lengths, so you can still tell which one is the long lead, or (+) in the next step.
On the back side of the fur, secure the LED by placing a button over the leads. Use a soft surface behind the LED (such as a yoga mat) to press the button into the back of the LED, and gently fold the leads down to the surface of the button. Keep track of which lead was the long lead, and mark the polarity with a '+' or a dot on that side of the button.
When folding the leads onto the button, you want to provide some structural stability and make it easy to solder to the two separate leads without causing an electrical short between them. So, it is recommended that you fold the leads away from each other, at right angles to the axis of the LED.
After the lights are secured with buttons, and the polarity is marked, trim the leads so that they extend almost to the edges of the button. Repeat this process for all lights.
Step 5: Prepare wire connections
First, make a chain of wires to connect all the (+) leads. Cut the wires in the lengths you will need, allowing at least 10-20% excess length (more slack may be needed for stretchy fabrics). Strip about 1/4" of the insulation away from each end of each wire and twist them together tightly in pairs, end to end in the order they will be joined to the lights. This step is easier if the spacing between all the lights is uniform. If your light spacing is variable, keep track of where the segments belong as you make them.
Pre-solder the twisted junctions, making a decent sized solder blob adhere to each twist. This step is much easier if you can clamp the twisted junction with a set of helping hands or similar device.
Make a second copy of this chain for the (-) leads.
As noted in the list of materials, it is strongly recommended that you use stranded insulated wire. Solid-core wire does not withstand repeated flexing very well, regardless of wire thickness. If you use non-insulated wire or conductive thread, you will risk short-circuits when the wires move and touch each other.
Step 6: Attach wires to LED leads
If the wire has been prepared with a big enough solder blob, then you will not need to add solder in this step, making it easy to do with two hands.
The button should act as a heat barrier, and protect the fabric while you are soldering. Use caution to not drip hot solder on the faux fur (acrylic melts!).
Note that the wires are oriented so that the insulated wire adjacent to the solder joint is supported by the button, rather than hanging off the edge where it will be vulnerable to damage.
Join all the (+) leads with one chain of wires, and join all the (-) leads with a second chain. Trim sharp points as needed.
Step 7: Attach battery pack
If your battery pack does not have a built-in switch, and you would like to add one, you can insert a standard pushbutton or toggle switch at this stage. If you can't find a 3 cell AA holder, you can make one from a 4 cell holder by joining two of the battery contacts within one of the cells.
Step 8: Seal solder joints
The glue offers strain relief and electrical isolation, and will protect the electronics from exposure to moisture (sweat or rain) when the scarf is worn, and will provide some protection during washing. Overall, I'd recommend that you spot clean or hand wash the garment in cold or warm water, and dry it flat. This type of assembly will probably survive mild machine washing at cold temperatures, but the life of the garment will be reduced by repeated tumbling and twisting, and exposure to soap and other chemicals will eventually cause the LED leads to become corroded. Dry cleaning is not recommended.
Step 9: Build battery pocket, attach to lining
Position the pocket where it will go on the lining (near the battery pack) - sew the matching velcro strip on the lining, then sew the pocket in place.
You can substitute a button, snap, or other closure for the pocket, but it is important to have a way of keeping the battery pack from falling out and dangling, since this can damage the connecting wires.
Step 10: Finish sewing scarf lining
Machine sewing: Keep the electronics on the top side when you are sewing around the edge. This will help you keep track of the wires, and make sure you don't sew through them or get them caught on parts of the machine.
Hand sewing: Use heavy duty thread, and an overhand stitch.
After the fur and lining have been joined along three seams, turn the scarf right-side out.
Cut a small slash in the inner (lining) side of the pocket, and pass the battery pack or snap connector through this hole. Hand-sew the slash closed so the battery pack cannot fit through the hole again. Hand sew the remaining open edge of the scarf.